Spinal anesthesia using small amount of saxitoxin

ABSTRACT

Vertebrates can be anesthetized regionally by a subarachnoid administration of saxitoxin. The amount which should be administered in a preferred embodiment ranges between 0.25 and 10 micrograms.

United States Patent Adams et al.

SPINAL ANESTHESIA USING SMALL AMOUNT OF SAXITOXIN Assignee: Astra Pharmaceutical Products, Inc.,

Worcester, Mass.

Filed: Aug. 14, 1973 Appl. No.: 388,146

US. Cl 424/95; 424/253 Int. Cl A6lk 27/00 Field of Search 424/263, 95, 253

July 1, 1975 References Cited OTHER PUBLICATIONS Chemical Abstracts, Vol. 68, (1968), p. 7603lk. Chemical Abstracts, Vol. 63, (1965), p. l047ld.

Primary ExaminerV. D. Turner Attorney, Agent, or FirmBrumbaugh, Graves, Donohue & Raymond 5 7] ABSTRACT Vertebrates can be anesthetized regionally by a subarachnoid administration of saxitoxin. The amount which should be administered in a preferred embodiment ranges between 0.25 and 10 micrograms.

4 Claims, 1 Drawing Figure PATENTEU L N975 3, 892 y 847 FIG.

SPINAL ANESTHESIA IN SHEEP; SEGMENTAL REGRESSION VOLUME: Iml

o-O TETRACAINE-QZS SAXlTOXlN 3pq/ml SPINAL SEGMENTS 1 SPINAL ANESTHESIA USING SMALL AMOUNT OF SAXITOXKN The present invention relates to a method of obtaining spinal anesthesia (i.e., by injection of an anesthetic into the subarachnoid space which contains the cerebro-spinal fluid) and a pharmaceutical preparation which can be used with this method. The invention particularly concerns novel uses for saxitoxin.

Toxins from marine sources of extraordinary potency have been known for many years. Saxitoxin is extracted from the Alaska giant butterclam, .S'uxidomusgigarzreus. Other terms by which the substance is known are clam toxin, mussel toxin. and shellfish toxin. The toxin. despite its name, does not originate in the clam or mussel in which it is found. It is believed to come from an algae, ofthe genus Gonyaulax from which a toxin identical to saxitoxin has been obtained. However, it is still not certain if this is the only source of the toxin in the Alaska butterclam.

The structure of saxitoxin has not been determined with certainty. lts hydrochloride is given the empirical formula C H N OQHCL According to published literature, the toxin most probably has a perhydropurine nucleus in which are incorporated two guanidinium moieties. (J. L. Wong et al., J. Am. Chem. Soc. 93, 7344 (l97l).

ln a voltage-clamped giant axon from the squid or lobster, local anesthetics such as procaine and cocaine reduce both inward initial sodium current and owutward potassium current. lnward sodium current can be reduced or even obliterated with saxitoxin, while the outward potassium current is totally unaffected.

Saxitoxin has not hitherto found any practical use as an anesthetic. While this compound can be used to induce nerve blocks in laboratory animals, the anesthetic dose is slightly below the lethal dose, which has preeluded, as a practical matter, the use of the compound as an anesthetic in its own right. M. H. Evans, Toxicon. 1968, Vol. 5, pp. 289-294, tested its use topically on peripheral nerve branches and exposed dorsal and ventral spinal roots in anesthetized cats, and found blocks in the latter case but concluded that the impermeability of the connective tissue sheath of peripheral nerves seemed likely to preclude its use as a local anesthetic agent.

Combinations of saxitoxin with a local anesthetic compound have been found to possess unusual anesthetic properties. This is manifested most significantly in improved longevity of action of combinations of the toxin with local anesthetics. In these combinations, saxitoxin is used in concentrations below that which produce reliable nerve blocks, and well below the toxiclevel. It is theorized that the local anesthetic enables the saxitoxin to penetrate the sheath surrounding the nerve roots and produce local anesthesia.

The present invention relies upon a subarachnoid spinal administration into the intact mannal ofa composition which consists essentially of small amounts of saxi toxin. It is not therefore necessary to combine these compounds with a local anesthetic, and it has been found that very low doses of the compounds give a longer duration of anesthesia than is obtainable with the use of certain prior art anesthetics of differing composition. Subarachnoid anesthesia in mammals, including man, is contemplated. For example, it is possible to obtain blocks of 4 hours and longer in duration with doses as small as 23 #g. By contrast, subarachnoid administration of tetracaine (at larger doses of 320 mg) gives a block of only from 1.5 to 3 hours and lidocaine (at much larger doses of 50 mg) gives blocks of merely from 1 to 2 hours, P. C. Lund, Principles and Practice of Spinal Anesthesia. pp. 420 and 425 (Charles C. Thomas, publisher, l97l These known spinal anesthetics cause more irritation and have a greater local toxicity than the composition used in practicing the present invention.

It has been found that the subarachnoid administration of the pharmaceutical composition used in the present invention should deliver a preferred dosage of approximately 0.25 to l0 micrograms of the compounds into the subarachnoid area of the spinal column for effective anesthesia to be induced.

The active compound saxitoxin, is preferentially carried by either a hypobaric, an isobaric, or a hyperbaric solution. Hypobaric solutions can be prepared using, e.g., triple distilled water as the vehicle for the drug. lsobaric solutions are usually prepared by using cerebrospinal fluid as the vehicle but sodium chloride added in a suitable concentration to an aqueous solution of the compound can also be used to obtain isobaricity. Hyperbaric solutions can be prepared by addition of varying amounts of glucose (usually 5-107c) to a water solution of the compound. A hyperbaric solution. the most commonly used preparation. can be easily formulated so that the pharmaceutical composition containing the compound used in the present invention can be controlled by gravity within the cerebrospinal fluid, i.e.. by tilting the patient head upwards or head downwards from the horizontal plane. The hyperbaric solution enables the anesthesiologist to control the movement of the anesthetic and thereby the extent of anesthesia in a manner that is well known in the art. The acidity of the solution described above is kept inside limits that give good stability to the saxitoxin.

If desired, addition ofa vasoconstrictor, e.g. epinephrine, to the pharmaceutical preparation can also be made in manners that are well known in the art. The concentration of active ingredient is generally 0.25l0 micrograms/ml and volumes of approximately l-6 ml of solution are injected into the cerebrospinal fluid contained in the subarachnoid space of the vertebrate to be anesthetized. The type of solution to be used, the concentration and volume to be administered are dependent on such factors as, for instance, age and size of the patient and on the surgical procedure to be performed.

The following examples show the invention in practice:

EXAMPLE 1 This example illustrates pharmaceutical compositions and methods for preparing them which are hypobaric solutions containing L0, 2.0 3,0, 4.0, 5.0, 6,0, 8.0, and 10.0 ug/ml saxitoxin dihydrochloride; pH 3.55.0.

Concentration #g/ml 1 2 3 4 5 6 8 10 Component Amount Saxitoxin dihydrochloridc i0 3O 40 5O 60 80 100 (mg) Hydrochloric acid.

ZN If necessary to adjust pH Sodium hydroxide.

2N if necessary to adjust pH Water for injection USP XVlll Sufficient quantity to make 10 liters The saxitoxin dihydrochloride is dissolved in a small amount of water and is diluted to a volume of 9.5 liters. The pH is adjusted and a sufficient volume of water is added to make a solution of 10 liters which is then sterilized.

EXAMPLE 2 This example illustrates pharmaceutical compositions and methods for preparing them which are isobaric solutions containing 1.0. 2.0. 3.0. 4.0. 5.0. 6.0. 8.0 and 10.0 ,LLg/mi saxitoxin dihydrochloride; pH 3.5-5.0.

Concentration g/ml l 2 3 4 5 6 a 10 Component Amount Saxitoxin i0 20 $0 60 so 100 dihydrochloride (mg) Sodium chloride 90 90 9o 90 90 90 90 90 USP XVll (g) Hydrochloric acid.

2N lf necessary to adjust pH Sodium hydroxide.

2N If necessary to adjust pH Water for injection USP XVlll Sufficient quantity to make 10 liters.

The saxitoxin dihydrochloride is dissolved in a small EXAMPLE 4 'd is a ded and water q i f wfiter Sodlum Chlon e d Four sheep weighing between 24 and 59 kg and of for lnjCCtlOn is added to a total volume of about 9.5 lit Aft l of the salt the H is adusted and approximately 4.5 to 5 months of age were treated with g ft er i volume of eater isjadded to saxitoxin (0.25. l and 2 micrograms). All sheep were i g h m St d restrained with their lumbar and thoracic spine in horima e a 0 l ers w en en zontal position during the subarachnoid injection. EXAMPLE 3 which was made over a period of 5 to l0 seconds using This example illustrates pharmaceutical composia 22 gauge-3 inch spinal needle at the interspace betions and methods for preparing them. which are hy- 50 tween the sixth lumbar and first sacral segments. The perbaric solutions containing 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, sheep were then immediately tilted so that the slope of 8.0 and l0.0 ag/ml saxitoxin dihydrochloride; pH the lumbar and thoracic spine was positioned lO.to the 3.5-5.0. horizontal (caudal inferior).

Concentration ug/ml l 2 3 4 5 5 8 10 Component Amount Saxitoxin l0 20 30 40 50 50 I00 dihydrochloride (mg) Dextrose.

anhydrous 500 500 500 500 500 750 500 500 USP XVIll (g) Hydrochloric acid. 2N If necessary to adjust pH Sodium hydroxide.

2N If necessary to adjust pH Water for injection USP XVlll Sufficient quantity to make 10 liters TABLE 1 sacral vertebral interspace of the sheep. 1.0 ml of 0.25% tetracaine. the most commonly used spinal anesthetic in humans. and 1.0 ml of 3 rig/ml of saxitoxin were administered to separate animals. The most commonly used concentration of tetracaine in spinal anesthesia. which is the most commonly used anesthetic in humans, as indicated by Lund (Principals and Practice of Spinal Anesthesia, C. C. Thomas Publishers, Springfield. 111., (1971) p. 420) is 0.25 0.3%. Above this 10 concentration the drug becomes increasingly irritating Spinal Anesthesia in Sheep with Saxitoxin Volume 1.0 ml

Duration of Block Concentration Onset Anal Vulval Digital Regression Sheep Wt. Drug Time Pain Pain Pain 2 Dermatomal Full Overt No. Kg. (pg/m1) (min) (min) (min) (min) Segments Recovery Effects l 46.0 0.25 3-5 150 150 75 90 150 min None 2 59.0 1.0 2 200 200 150 100 3 hrs None 24 hrs 3 25.0 2.0 2-4 270 270 230 150 5 hrs None 24 hrs 4 24.0 2.0 5 120 120 120 Not 2 hrs None Measured 24 hrs A series of four additional sheep were tested using a 3 microgram dose of saxitoxin. Table 11 shows the results that were obtained:

and is not generally used. In man the injection is usually made between either the second and third or third and fourth lumbar interspaces. The drug, after injection,

TABLE 11 Spinal Anesthesia in Sheep Drug: Saxitoxin Dose: 3 ug Vol.1 1 m1. Injection site: L6-S1 Spon- Average tane- Segmental ous Cephalad Vulva or Muscle Regression S read Anal Scrotum Flexor Activ- Wt. Full 2 Segments C ephalad rom ity Shee Wt. Onset Re- Re- Re Digital Rear Sup- Reor More Spread Point of No. Sex (k) (min.) flex Pain flex Pain flex Pain Leg port covery Left Right Left Right Injection 400 120 60 S1 S1 26 F 23.8 4 280 280 210 210 70 80 80 400 24 hr. 390 29 M 28.4 4 170 180 80 70 60 60 50 155 40 70 S1 S1 0 31 F 24.3 65 65 40 50 60 60 I5 80 300 40 50 L6 L6 1 625180325180 32 F 40 S3 S2 0 hr. hr. hr.

Notes:

Time in minutes except where indicated.

Segmental spread in the lumbar (L) or sacral (S) regions and regression were measured by observing the response to pinching of the pura ertebral skin.

Time for regression of one segment was 60 min.

FIG. 1 is a graph showing the spread and effect of the subarachnoidally administered local anesthetic, versus time after administration.

Using the technique described in the foregoing example, the local anesthetic drug to be tested was injected into the subarachnoid space (which contains the cerebro-spinal fluid. between the sixth lumbar and the first mixes with the spinal fluid and is carried or spread anteriorly and posteriorly.

On the Y axis (the ordinate) of FIG. 1 is a schematic representation of the segments of the spinal cord. 1n the 65 sheep, caudal to cephalad (posterior to anterior) the segments of the spinal cord are: coccygeal 3,2,1; sacral 4,3,2, 1; lumbar 6,5,4,3,2,1; thoracic -l 3,l2.l l.lO.9,8.7.6.5.4.3.2.l; cervical 7.6.5.4321. Lumbar 6 is the only one of the last three groups illustrated or represented in FIG. I.

Depending on many factors such as concentration. volume of solution. manipulation of the patient. and inherent characteristics of the drug. a variable degree of duration and spread of anesthesia can be achieved. This spread and its recovery or so-called regression is pictorially represented as in FIG. 1. Above (or anterior to) each point there is no anesthesia and the spinal nerves are unaffected by the drug. Below each point all spinal segments or nerves are blocked. Over a period of time. which is represented on the abscissa or X axis of FIG. 1, the anesthesia wears off beginning anteriorly (because less drug has reached these nerves) and progresses posteriorly until total recovery occurs. Each point value in FIG. I therefore represents the level of anesthesia at a particular time and also the total number of spinal segments which are blocked at that time. FIG. 1 compares the level of anesthesia and the segmental regression pattern obtained in sheep after administration of each of the two local anesthetics.

The graphs in FIG. 1 show that initially the two local anesthetics tested both blocked nerve conduction in a total of seven spinal segments. After three hours. however, saxitoxin continued to provide anesthesia at at least four segments (everything below 5-4). whereas tetracaine had completely regressed. Saxitoxin required five hours to regress (the point at which the animal had completely recovered). Moreover. tetracaine provided anesthesia and pain relief at segments below 5-4 for only about l.5 hours. whereas saxitoxin at that level provided anesthesia and pain relief for three hours.

Recovery of function in the animals tested was complete and no sequelae followed the long duration of anesthesia caused by saxitoxin.

Upon reading the foregoing description. persons in the art will become aware of a number of modifications that can be made to the invention described herein without the exercise of inventive skill. These modifications are intended to be included within the scope of the invention. and the foregoing is intended to be merely illustrative of certain preferred embodiments of the invention. The appended claims define the scope of protection sought.

We claim:

1. A method for anesthetizing a mannal comprising administration by injection into the subarachnoid space of the intact mannal. a pharmaceutical composition containing saxitoxin as active ingredient in amount effective for producing anesthesia.

2. The method as claimed in claim 1 wherein the amount of saxitoxin which is administered to the mannal is between about 0.25 and l0 micrograms.

3. The method as claimed in claim 1 wherein the amount of saxitoxin which is administered to the mammal is between 3 and 6 micrograms.

4. A method for inducing spinal anesthesia in a mammal compromising administration by injection into the subarachnoid space of the intact mammal, from I to 6 milliliters of a pharmaceutical composition comprising a compatible vehicle and as the active ingredient saxitoxin in concentration from 0.25 to 10 pg per milliliter of the vehicle.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,892,847

Herbert J.F. Adams, Murray R. Blair, Jr. Robert N. INVENTOWS) I Boyes, Maxim I. Lebeaux and Helen G. Vassallo It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

First page, Item [54] and Col. 1, line 1,

"AMOUNT" should read --AMOUNTS;

II II Col. 1, line 22, C H N O 2HCl should be C H N 0 2HCl Col. 1, lines 29 & 30, "owutward" should read outward; Col. 1, line 57, "mannal" should read -mammal; Col. 3, line 51, delete "6.0,"; Cols. 5 & 6, in Table II, delete all figures under the heading "Anal" with respect to Sheep No. 32, and substitute the following figures:

Reflex Pain 180 180 20 20 hr. hr. Col. 8, line 14, "mannal" should read --mammal-; Col. line 16, "mannal" should read --mammal;

Col. 8, line 18, after "anesthesia" insert in association with a pharmaceutically acceptable carrier-;

Col. 8, lines 20 & 2l, "mannal" should read --mammal; and

Col. 8, line 26, "compromising" should read comprising-.

Signed and Sealed this tenth D3) of February 1976 [SEAL] Attest:

RUTH C. MASON Arresting Officer C. MARSHALL DANN (ommixsiuner oj'Parenrs and Trademarks 

1. A METHOD FOR ANESTHETIZING A MANNAL COMPRISING ADMINISTRATION BY INJECTION INTO THE SUBARACHNOID SPACE OF THE INTACT MANNAL, A PHARMACEUTICAL COMPOSITION CONTAINING SAXITOXIN AS ACTIVE INGREDIENT IN AMOUNT EFFECTIVE FOR PRODUCING ANESTHESIA.
 2. The method as claimed in claim 1 wherein the amount of saxitoxin which is administered to the mannal is between about 0.25 and 10 micrograms.
 3. The method as claimed in claim 1 wherein the amount of saxitoxin which is administered to the mammal is between 3 aNd 6 micrograms.
 4. A method for inducing spinal anesthesia in a mammal compromising administration by injection into the subarachnoid space of the intact mammal, from 1 to 6 milliliters of a pharmaceutical composition comprising a compatible vehicle and as the active ingredient saxitoxin in concentration from 0.25 to 10 Mu g per milliliter of the vehicle. 